PROJECT SUMMARY Exercise is among the most effective interventions for maintenance of metabolic fitness and prevention of chronic disease including age-related sarcopenia, insulin resistance, cognitive decline and limb/organ ischemia. Despite these benefits of exercise, certain populations who would benefit most from exercise interventions, such as older individuals with peripheral artery disease, are unable to safely exercise, leaving surgery as the only option. Many others who could benefit from exercise choose not to, or fail to maintain exercise as part of a beneficial lifestyle change. Thus, the identification and characterization of functional exercise mimetics on a molecular level could inform future treatments to improve metabolic health, particularly in the elderly. Dietary methionine restriction (MR) is best known for lifespan extension, loss of adiposity, and improved glucose handling in model organisms similar to calorie restriction, but without enforced restriction of food intake. Mechanisms underlying MR benefits are poorly understood, but thought to require upstream amino acid sensing through the GCN2/eIF2?/ATF4-dependent integrated stress response. Despite the strong phenotypic overlap between MR and exercise, the effects of MR on skeletal muscle are largely unexplored. My preliminary data suggest that MR acts within weeks as an exercise mimetic, improving endurance exercise capacity in untrained young and old male mice likely through increased mitochondrial number and activity. Here, I propose to test the hypothesis that MR induces oxidative phosphorylation, mitochondrial biogenesis and improved endurance exercise capacity via activation of the GCN2/ATF4-dependent pathway specifically in skeletal muscle fibers in both young and old male and female mice. Elucidation of a molecular connection between this amino acid sensing pathway and mitochondrial number and function would represent a novel finding with translational implications, particularly in the elderly. The proposed research will take place in the laboratory of James Mitchell in the Dept. of Genetics and Complex Diseases at the Harvard T. H. Chan School of Public Health. The Mitchell lab has years of experience with dietary amino acid manipulation in rodent models, and funding from the NIA and NIDDK to study the effects of MR on aging, glucose homeostasis and stress resistance, and all of the relevant equipment and expertise to analyze the effects of MR on skeletal muscle function in vivo and in vitro models. The training will involve work primarily towards my PhD thesis, including execution of the proposed experiments, analysis of the data, presentation at local and national meetings, writing of manuscripts and responses to reviewers? comments, and writing and defending my dissertation under the guidance of Dr. Mitchell. The local environment on the Harvard Longwood Medical Campus is an outstanding one for research in this area.